The present invention relates to a chuck. More particularly this invention concerns a lever-action chuck of the type used to hold the ends of a crankshaft as same is being machined.
A standard lever-action chuck for use in a lathe or the like has a body adapted to be rotated about a chuck axis and formed with a plurality of axially forwardly open passages each having a pair of angularly confronting side faces. Respective guides in the passages are pivotal in the body about respective guide axes extending secantally of the axis, that is about axes that are offset from the chuck axis and that each lie in a plane generally perpendicular to the chuck axis. Respective elongated jaw arms axially slidable in the guides each have a pair of angularly oppositely directed side faces riding on the respective passage side faces. Means is provided to axially displace the jaw arms between outer positions with their outer ends spaced forward from an end face of the chuck body and inner positions with their outer ends closed to or even recessed in the end face of the chuck body. Further means is provided for pivoting the jaw arms about the respective secantal guide axes so that, in the outer position, the outer arm ends can pivot in to grip a work-piece.
Such chucks are typically used in axially confronting pairs to rotate a workpiece such as a crank shaft that is gripped at both ends and rotated about the coaxial chuck axes to machine bearing and crank surfaces of the crankshaft. The retractability of the jaw arms makes it possible to load the workpiece into the chucks and remove it from them radially of the machining axis without having to axially displace the chucks. The pivotability of the jaw arms makes it possible to clasp them on the workpiece without applying an axial force to the workpiece, which force could distort it.
The main problem with this type of chuck is in accurately fitting the jaw arms to the chuck body. They are normally of square or rectangular section and are supported on their radially inner and outer surfaces in the guides and on their angularly oppositely directed side faces directly on the side walls or faces of the passages. Thus these passages must be meticulously machined in the chuck body. Any error during the machining results in a ruined workpiece. Furthermore once the chuck wears somewhat, it must normally be discarded as loose jaw arms cannot hold the workpiece perfectly on center as required in a precise machining operation.
It is therefore an object of the present invention to provide an improved lever-action chuck.
Another object is the provision of such an improved lever-action chuck which overcomes the above-given disadvantages, that is which is easier to manufacture and that has a longer service life than the known such lever-action chuck.
A chuck has according to the invention a chuck body adapted to be rotated about a chuck axis and formed with a plurality of axially forwardly open passages each having a pair of angularly confronting side faces, respective guides pivotal in the passages about respective guide axes extending secantally of the chuck axis, and respective elongated jaw arms axially slidable in the guides. Each jaw arm has a pair of oppositely angularly directed side faces angularly confronting and spaced from the respective passage side faces. A respective guide plate in each of the passages has an outer face engaging one of the respective passage side faces and an inner face engaging the respective arm side face. These plates are releasably fixed in the passages.
Thus with this system the critical side faces of the guide passages, which are subject to considerable stress during machining as the chuck is rotated at high speed, are made somewhat oversize. The guide places are subsequently fitted to them to achieve a perfect fit of the jaw arms, allowing any mismatches to be easily compensated for.
According to the invention a pair of the guide plates angularly flanks each of the jaw arms in each of the respective passages. Thus both side face of each jaw arm are accurately guided and supported on a respective such guide plate.
Furthermore each passage side face is formed with a seat in which the respective guide plate is fitted with the side face of each of the guide plates projecting angularly inward into the respective passage past the respective passage side face. Respective screws having heads bearing on the chuck body and shanks threaded into the guide plates fix the plates in the seats. The guide plates are rectangular and the faces are planar and extend parallel to the chuck axis.